Purple Line Officials Show Off Noise Mitigation Techniques In Town Of Chevy Chase

The Town of Chevy Chase will be the only section of the planned 16-mile Purple Line light rail that includes noise walls, a fact transportation planners emphasized on Wednesday in an attempt to quell noise concerns from residents.

It’s unclear if it worked.

After a roughly hour-long presentation that delved into the science of federal transportation noise requirements and included various soundbites of what a passing Purple Line train car might sound like, some at the meeting held in the Town of Chevy Chase’s Town Hall remained skeptical.

A few residents with houses backing up to or near where the Purple Line would run said readings of existing ambient noise levels (which provide a baseline for how much noise can be added via a train) were inaccurate. One asked Purple Line project manager Mike Madden if any more noise mitigation measures would be added, or if she should start looking at moving away.

The presentation, one Madden said the Maryland Transit Administration had never made before in a public meeting, was coordinated by the Town’s Purple Line Mitigation Advisory Group (MAG). A number of homes in the Town on Elm Street, Oakridge Lane and Lynn Drive back up to the existing Capital Crescent Trail.

The Town’s official opposition to the now $2.2 billion (and still unfunded) east-to-west light rail has softened in the last few years. Madden praised MAG for providing input that has led to design improvements he said would not have been possible otherwise.

About eight residents let the Maryland Transit Administration’s noise consultant place decibel measuring devices on their property to record existing ambient sound. The consultant, Pennsylvania-based noise engineer Ahmed El-Aassar, made a series of readings in May that showed the typical average decibel level on the properties closest to the Purple Line route ranged from 50 to 60 decibels.

A passing Purple Line train, which would include noise-mitigating car skirts that cover part of the wheels and the four-foot noise wall, would generally mean decibel levels around 60 decibels. El-Aassar said that left all but one property in the Town safely within the Federal Transit Administration’s criteria for noise levels.

Madden said the noise walls aren’t required in most parts of the Town. El-Aassar said the bodyside skirts on the vehicle account for an eight-decibel reduction. The noise wall, which would be a minimum of four feet tall on the south side of the rail, would mean a further four-decibel reduction.

Residents will have more opportunity to comment on noise mitigation when the Final Environmental Impact Statement comes out, which Madden said is scheduled for this summer.

The video above shows El-Aassar demonstrating what a passing train would sound like from the back of one home in the Town without the four-foot noise wall and then with the four-foot noise wall. The first two trains that pass in the illustration are without the noise wall. The third passing train includes the noise wall.